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Guidelines for Earthwork in Railway Projects

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GOVERNMENT OF INDIA MINISTRY OF RAILWAYS

GUIDELINES FOR EARTHWORK IN RAILWAY PROJECTS

Guideline No. GE: G-1

July 2003

Geo-technical Engineering Directorate, Research Designs and Standards Organisation

Manak Nagar, Lucknow – 11

Including ACS 1

idHighlight


FOREWORD

The Railway track system is an important part of the transportation infra- structure of the country. Coupled with economic growth of our great country, the Railways have to carry ever-increasing traffic by augmenting the existing capacities in terms of higher axle loads as well as greater speeds. This calls for a sound track system, both superstructure and substructure.

RDSO has been involved with research and standardization aspects of substructure for the last few decades. Various guidelines have been issued from time to time covering different aspects of track foundation. There have been numerous correction slips added with the experience gained. However, the practice in the field shows wide variations from one railway to the other, some of which may be attributable to lack of clarity on many aspects of geo-technology. Accordingly, a committee of experts was formed to compile the various instructions, correction slips and reiterate some of the neglected aspects of construction/maintenance practices.

I am happy to see that this book containing detailed guidelines for earthwork in Railway Projects draws upon the past experience and developments in other parts of the world in order to pass on the right and adequate knowledge to the field engineers concerned both with construction as well as maintenance aspects. It is particularly heartening to see the right emphasis on quality control by incorporation of the details of field tests and various formats and proforma through which quality can be monitored at different levels.

I am sure the book will be found very useful by all sections of Civil Engineers. Your feedback may be sent directly to Exe. Dir.(GE), RDSO or Exe. Director (P), Railway Board, who will be glad to take care of your doubts and suggestions.

June 2003 Member Engineering Railway Board, New Delhi.

(i)


PREFACE

Performance of a track primarily depends on the soundness of its foundation. To keep maintenance requirements low and have good riding quality, its formation should be adequately designed to cater for envisaged traffic loads and constructed with modern and appropriate techniques. Already large lengths of formations constructed earlier as well as recently, are showing signs of distress under present level of traffic. These lengths are likely to increase manifolds with the introduction of higher axle loads, speeds and enhanced GMT.

Geo-technical Engineering Directorate of RDSO had already issued Guidelines for execution of earthwork in Railway projects in year 1970, which were revised subsequently, in year 1978 and 1987. Guidelines for earthwork in conversion projects were also issued in 1995. Further addition in knowledge and experience in field of geo-technical engineering brought the need for revision and amalgamation of various relevant Guidelines into one. Railway Board asked RDSO to revise existing Guidelines for earthwork in Railway project to avoid duplication of provisions and curtail multiplicity vide Railway Board's letter no. 94/CE-II/MB/6 dated 27.8.2001. A draft revised Guidelines had been prepared and sent to the Railway Board by RDSO. Vide letter no. 94/CE-II/MB/6 dt. 5.12.2001, 12.02.2002 & 15.04.2002, Railway Board nominated a committee of following officers for revision of existing Guidelines:

Name Designation Shri V. K. Jain Chief Engineer (General), Northern Railway

Convenor Shri Pramod Kumar Executive Director (General), Civil Engg., Railway Board

Member Shri S. K. Raina Executive Director, Geotechnical Engineering, RDSO

Member Shri Abhay Kumar Mishra Chief Engineer (Central), Northern Railway

Member

On the basis of the discussion held in various meetings of this committee, the final revised Guidelines was prepared. The committee was rendered valuable suggestions and assistance from S/Shri Ashok Kumar Mishra, Director/GE, and S. K. Awasthi, ARE/GE, RDSO during deliberation and preparation of this booklet.

These Guidelines now cover briefly all aspects of design and construction of earthwork in New lines, Doubling, Gauge conversion and Rehabilitation works. This also incorporates all the correction slips already issued till date. These guidelines emphasise on provision of blanket layer of different thickness on formation based on experience and behaviour of different type of subgrades under repetitive loading and recommends mechanical execution of earthwork with emphasis on quality control of earth work. The guidelines has been made more user friendly by incorporating basic design details and standard formats for control of quality etc. It is expected that the revised guidelines will enable Engineers on Indian Railway to achieve awareness and quality in execution of earthworks in Railway formations.

July 2003 (S. K. Raina) RDSO, Lucknow (ii) Executive Director, Geotechnical


CONTENTS

S. No. Title Page No. 1. Preamble 1 2. Definitions 1 3. Soil Exploration & Surveys 2 4. Design of Railway Formation 7 5. Materials for construction 14 6. Execution of Formation Earthwork 15 7. Quality Control of Earthwork 28 8. Maintenance of Records 32 9. Association of RDSO for Quality Assurance in Construction Projects 33 10. References 33

SKETCHES A. Broad gauge track showing the nomenclature of various items B. Specification for Blanket Materials C. Minimum Recommended Formation Width for Banks/Cuttings D. Limits in the Gradation Curves Separating Liquefiable and non-liquefiable soils E. Details of Side Drains and Catch water Drains in Cuttings F. Scheme for Bank Widening showing Benching and Sandwich Construction G. Typical embankment profile for Sandwich construction with cohesive soils H. Sampling Patterns for Check of Compaction I. Details of Backfill on Bridge Approach

ANNEXURES

I. Brief Details of Soil Classification II. Relevant paras of Engineering Code III. Procedure for Slope Stability Analysis IV. Field Compaction Trial V. Compaction Characteristics of different materials VI. Proforma for Maintenance of Records VII. Summary of Quality Control Tests VIII. Salient Features of Vibratory Rollers IX. List of Relevant IS codes X. List of Equipments In Field Laboratory

(iii)


GUIDELINES FOR EARTHWORK IN RAILWAY PROJECTS

1.0 PREAMBLE

Extensive research work has been done to identify the most efficient, economic and suitable design and construction procedure for a sound and trouble-free railway embankment. While most of the work has been done in relation to earth dams, experience with rail–road construction indicates that the provisions of the guidelines issued earlier (for new construction as well as gauge conversion) in 1987 and 1995 need elaboration and updating.

Various studies done on Indian Railways indicate that large lengths of railway formation are of failing type and huge resources are being consumed for maintenance of track in order to ensure the safety of the traffic.

In view of this scenario, it is felt necessary to update various guidelines on the subject and to combine guidelines issued earlier into a single guideline for the benefit of field Engineers.

2.0 DEFINITIONS

For the sake of clarity, a few commonly used terms with their specific meanings are explained in sketch-A, showing cross section of a BG track.

2.1 Track Foundation: Constitutes ballast, blanket and subgrade, which is placed / exist below track structure to transmit load to subsoil.

2.2 Ballast: Crushed stones with desired specifications placed directly below the sleepers.

2.3 Sub-ballast: Sub-ballast is a layer of coarse-grained material provided between blanket/subgrade and ballast and confined to width of ballast section only. However, sub-ballast is not in vogue on Indian Railways. Therefore, its provision has not been considered in these Guidelines.

2.4 Blanket: Blanket is a layer of specified coarse, granular material of designed thickness provided over full width of formation between subgrade and ballast.

2.5 Sub-grade: It is part of embankment/cutting provided above subsoil by borrowed soil of suitable quality upto bottom of blanket/ballast.

2.5.1 Cohesive Subgrade: Subgrade constructed with soils having cohesive behaviour i.e., shear strength is predominantly derived from cohesion of the soil is termed ascohesive subgrade. Normally, soils having particles finer than 75 micron exceeding 12% exhibit cohesive behaviour. As per IS classification, all fine-grained soils and GM, GM-GC, GC, SM, SM-SC & SC types of soils exhibit cohesive behaviour.


Note: Soil classification in these Guidelines is as per IS: 1498-1970. For ready reference, brief details of soil classification, as per IS: 1498 are given at Annexure-I.

2.5.2 Cohesionless Subgrade: Subgrade constructed with cohesionless, coarse-grained soils i.e., shear strength is predominantly derived from internal friction of the soil are termed as cohesionless subgrade. Normally, soils having particles finer than 75 micron less than 5% exhibit cohesionless behaviour. As per IS Classification, GW, GP, SW & SP types of soils fall in this category.

2.5.3 Other types of soils, which have soil particles finer than 75 micron between 5 to

12%, need detail study for ascertaining their behaviour. 2.6 Dispersive Soil: Dispersive clayey soils are those, which normally deflocculate

when exposed to water of low salt content. Generally, dispersive clayey soils are highly erosive and have high shrink and swell potential. These soils can be identified by Crumb, Double Hydrometer, Pin Hole and Chemical Tests.

2.7 Formation Top: Boundary between ballast and top of blanket or subgrade (where

blanket layer is not provided). 2.8 Cess: It is part of top of formation from toe of ballast to edge of formation. 2.9 Formation: It is a general term referring to the whole of blanket, sub-grade and

sub-soil. 2.10 Sub-soil: Soil of natural ground below subgrade. 2.11 Unstable Formation: It is yielding formation with non-terminating settlement

including slope failure, which require excessive maintenance efforts. 3.0 SOIL EXPLORATION & SURVEY 3.1 Objectives of constructing a stable formation can only be achieved if soil

exploration, as envisaged in Engineering Code Paras E--409, 425 and 528, is undertaken in right earnest and precautions are taken to design bank & cutting against likely causes which could render it troublesome during service. The above referred paras of Engineering Code have been reproduced in Annexure-II.

3.2 Adequate provision for soil surveys & explorations at different stages, as per

requirements of the terrain, should be made in the project estimates to cover the cost for this activity.

3.3 Objectives of Soil Exploration: Main objectives of soil survey and exploration work are:

a) to determine soil type with a view to identify their suitability for earthwork in formation and to design the foundation for other structures.


b) to avoid known troublesome spots, unstable hill sides, swampy areas, softrock areas, peat lands, etc.

c) to determine method of handling and compaction of subgrade.d) to identify suitable alignment for embankment and cutting from stability,

safety, economy in construction and maintenance considerations.e) to identify suitable borrow area for desired quality and quantity of subgrade

and blanket material.f) to determine depth of various strata of soil and bed rock level.g) to determine ground water table position and its seasonal variation and general

hydrology of the area such as flood plains, river streams, etc.h) to determine behaviour of existing track or road structure nature and causes

of geo-technical problems in them, if any.

3.4 Soil survey and exploration for construction projects should be carried out in following three stages:

3.4.1 Soil Investigation during Reconnaissance Survey

a) The main objective of soil survey during Reconnaissance is to collect maximumsurface and sub-surface information without drilling exploratory boring/ test pitsto avoid obviously weak locations such as unstable hill sides, talus formation,swampy areas, peat grounds, very soft rocks or highly weathered rocks, etc.

b) At reconnaissance stage, available data from geological and topological maps andother soil surveys done in past, existing soil profiles in nearby cuts, quarries arescrutinized. Water table is recorded from local observation and inquiry. Theinvolved soils are classified by visual examination and if necessary, few field/laboratory tests are conducted for this purpose.

c) Survey reports available from other Departments/Agencies such as GeologicalSurvey of India, Ministry of Road Transport and Highways, Central Board ofIrrigation and Power, CPWD, State Irrigation, PWD, etc. can be acquired to obtaininformation on the accessibility, geology and soils, subsurface information, etc.

d) Areas of prospective borrow soil and blanket material should also be surveyed togive idea of quality and quantity of materials to be used for construction ofRailway embankment.

e) Above collection of data should be incorporated in the Feasibility Report requiredto be submitted as per para 576 and 555 in chapter of Project Engineering underheading of formation (para 528 of Engineering Code).

f) The data and information collected during survey should be presented in suitableformat such as graphs, bar chart or in tabular or statement form.


3.4.2 Soil Investigation during Preliminary Survey a) Primary objective of preliminary exploration is to obtain sufficient subsurface

data to permit selection of the type, location and principal dimensions of all major structure and estimation of earthwork and design of formation. The scope of preliminary survey is restricted to determination of depths, thickness and composition of each soil stratum, location of rock and ground water and also to obtain appropriate information regarding strength and compressibility characteristics of various soil strata.

b) As stated in Para E-409 of Engineering Code, the field work in Preliminary

Survey includes a compass traverse along one or more routes with transverse and longitudinal levels to prepare a L- section of routes proposed. This fieldwork shall also cover a soil survey by sampling at suitable intervals in order to obtain a fair idea of the soil classification and characteristics of soils on proposed routes. Testing of disturbed soil samples is usually adequate, however core drilling will be necessary in rocks. This will help in determining thickness of blanket layer on different sections and total quantity of blanket material to be required.

c) Exploratory boring with hand/ auger samplers and soil sampling should be

undertaken along the alignment and soil samples also should be collected from borrow pit area, at an interval of 500 meter or at closer interval, wherever change of soil strata occurs. The boring should be done upto 1.5 to 2.0 m depth below existing ground level. In case of high embankment and problematic substrata, the boring should be taken down to a depth equal to twice the height of embankment. Samples should be collected from each stratum found in each boring.

d) Bore logs are prepared based on laboratory test results of disturbed samples

obtained by auguring or split spoon sampler. Particle size distribution, soil classification and index properties of the soils are determined from laboratory tests.

e) In case of soft clays and sensitive clays, in-situ vane shear tests should be conducted to determine its shear strength and depth of underlying compressible clay layer. Undisturbed tube samples should also be collected to know actual moisture content, natural dry density and shear and consolidation parameters of the soil.

f) Geo-physical investigations for bedrock profile, sub-surface strata and soil

properties are required to be carried out for foundation of major structures such as bridges. Methods such as Seismic Refraction Method (IS: 1892-1979), Standard Penetration Test (IS: 2131- 1981), Dynamic Cone Penetration Test (IS: 4968-1974) etc, will be required to be carried out to ascertain constituents of substrata and their properties and design foundation of such structures. In alluvial strata, deep auger boring upto 6m may be deployed for subsurface exploration and sampling.

g) The data and information collected during survey should be presented in suitable

format such as graphs, bar chart or in tabular or statement form.


3.4.3 Soil Investigation during Final Location Survey a) During Final Location survey, detailed investigations are done at locations where

important structures viz. high bank, deep cuttings, major bridges etc. are to be located and where weak sub-soil, swampy ground, marshy land exist. Undisturbed soil samples with the help of deep auger sampler or Split spoon samplers are collected for conducting detailed tests viz. shear strength tests & consolidation test to design safe and economical structure and predict settlements. However, if some tests during preliminary survey are deficient, the same should also be covered.

b) Assistance may be taken from Geologist, in case of rocky strata, known unstable

hill slopes, earthquake prone area and geological fault.

c) Detailed subsoil exploration is necessary to check stability of structures against failure and to predict anticipated settlement. Bores are made along alignment normally at 200 m to 300m apart in case of uniform type of soil and closely spaced in critical zones. Soil samples within the boreholes are obtained at every change of stratum and interval not exceeding 1.5 m. In case of sandy and gravely soils, Standard Penetration Test may be adequate, as taking out samples in these type of strata is difficult.

d) Besides classification tests, soil samples should be tested for shear strength and consolidation properties. In case of very soft clays, vane shear test should be conducted for each boring site. Free swell index test should also be carried out in case of expansive soil and organic contents of soil should be determined if soil is suspected to be having large organic contents.

e) Sources of blanket material of specified quality and its availability around project

site needs to be located to assess its realistic costs for inclusion in project estimates. The source identification should cover various logistics involved in its utilization.

f) The data and information collected during survey should be presented in suitable

format such as graphs, bar chart or in tabular or statement form. 3.5 Soil Survey & Exploration for Conversion, Doubling & Rehabilitation Work

For these projects, additional informations required will be as follows:

3.5.1 A statement listing out problematic stretches on existing track should be prepared/obtained after scrutiny of gang charts for identifying locations requiring frequent attentions, having unsatisfactory TRC results, past history of stretches having failure like slips, subsidence, pre-mature ballast recumbent, ballast penetration etc.

3.5.2 Failure of existing formation is accompanied by signs of distress/instability. The

identified and suspected locations shall be subjected to detailed examination as per symptoms of failures. Recommended scheme of soil exploration and testing are as under:


S. No

Symptoms Type of failure

Recommended Scheme for soil exploration and data collection

Soil testing

1 2 3 4 5 1

i) Bank settlement - loss of longitudinal profile ii) Heaving of soil beyond toe iii) Leaning of telegraph posts, trees , etc. on the bank and at the toe

Base failure

i) Recording of bank profiles and ballast profile in x-section ii)Undisturbed sampling iii) Field tests- Vane shear DCP/SPT

i) Classification tests ii)Consolidation tests iii) Natural moisture content and Natural dry density tests. iv) Peak and residual shear strength tests

2 i) Flattening of Bank/slope ii) Bulging of slopesurface. iii) Longitudinal crackson cess/slopes iv) Leaning of OHEmasts

Slope failure

i) Recording of bank profile and x-section of ballast profile. ii) Survey and recording of surface cracks iii)Undisturbed sampling

i) Classification and swell tests ii) Peak and Residual Shear strength tests iii) Natural moisture content and Natural dry density tests.

3 i) Soil heaving on cessand on slopes ii) Ballast penetrationexceeding 30 cm belowformation iii) Excessive – crosslevel variations

Subgrade failure (by shear)

i) Recording of bank and ballast penetration profiles inside subgrade ii) Collection of data a) Track geometry

variations b) Excessive

maintenance inputs c) Quantum of ballast

recoupment d) Speed restrictions

imposed iii) Undisturbed soil samples below the ballast penetration

i) Classification and swell tests ii) Shear strength tests iii) Natural Moisture content and Natural Dry Density tests

4 i) Fouling of ballast withsubgrade fines ii) Ballast penetrationbelow formation – 30 cmor less iii) Impaired drainage iv) Excessive cross levelvariations in Mansoon

Subgrade failure (by mud pumping)

i) Recording of bank profile and ballast penetration inside subgrade ii) Collection of data - a) Track geometry

variations b) Excessive

maintenance inputs

i) Classification and swell tests ii) Shear tests iii) Natural Moisture Content and Natural Dry Density tests


v) Hard running duringsummer

c) Speed restrictionsimposed

iii) Undisturbed soilsamples from below the ballast penetration

5 i) Reduced cess&Denuded slopes- loss ofsoil/absence of vegetation. ii) Formation ofrills/ gullies and pot holeson slopes & on cess

Erosion failure of slopes leading to ballast penetration and slope failure

i) Recording of bankprofile

ii) Disturbed soilsamples

i) Classificationtests ii) Field crumbtest for soil dispersivity iii) Pin hole testiv)Doublehydrometer tests v) NaturalMoisture Content and Natural Dry Density tests

6 i) Cut slope failures ii) Choked side drainsiii) Seepage of water.iv) Saturated subgrade

Failure of Cuttings

i) Recording of profileside slope, longitudinal drain sections, HFL and Ground water table

i) Classification ofsoils ii) Cross-sectionand Ballast penetration iii) NaturalMoisture Content and Natural Dry Density tests iv) Lab. Sheartests

Notes: a) In practice generally more than one type of failure is encountered. b) Recommended scheme and soil tests are for general guidance.

3.5.3 Frequency of soil sampling shall depend on the extent and type of problems in the troublesome stretches. However, samples should be taken at 500m intervals for determination of natural dry density and soil type only where no formation problem is reported.

3.5.4 In order to ensure proper bonding of earthwork and soil compatibility behaviour of old and new earthwork, samples of soils from mid-slope of existing bank at about 1 m depth and 500m length or closer intervals should be collected and tested for particle size, natural moisture content, natural dry density and consistency limits.

4.0 DESIGN OF RAILWAY FORMATION

4.1 In order to construct a formation that gives trouble free service under the most adverse conditions of loading, maintenance, and weather, it is necessary that:


(i) Sub-grade in bank or cutting is structurally sound so as not to fail in shear strength under its own load and live loads; and

(ii) Secondly, any settlement due to compaction and consolidation in sub-

grade and subsoil should be within the permissible limits. 4.2 Various Aspects of Designing a Sub-Grade & Subsoil

Subgrade should be designed to be safe against shear failure and large

deformations. Adequacy of subsoil against shear strength and settlement should also be examined.

4.2.1 Deficient Shear Strength of Sub-Grade &/or Sub-Soil leads to:

(a) Bearing capacity failure of sub-grade, resulting into cess and crib heave. Deep ballast pockets are formed as a result of such failures. Inadequate cess width is also responsible for initiation and enhancement of bearing capacity failure of subgrade.

(b) Interpenetration failure or mud pumping failure, resulting into vitiation of clean ballast cushion, and

(c) Slope failure, if factor of safety against slope stability is not adequate.

Therefore, subgrade/subsoil should be designed to ensure not to allow any shear failure.

4.2.2 Large Deformation without Shear Strength Failures of soil can be due to:

a) Poor compaction during construction and consolidation (primary and secondary) of subgrade and/or sub-soil; and

b) Settlement and heave due to shrinking and swelling characteristics of subgrade and/or sub-soil. The swelling and shrinkage characteristics of sub-soil shall be significant in cases where bank height is less than 1m or it is in cutting.

These aspects should be taken into account at the time of construction to avoid

large settlement causing maintenance problems and leading to formation failure. 4.2.3 Top Width of Formation:

(a) It should be adequate enough to accommodate track laid with concrete sleepers and standard ballast section and have minimum 900mm cess width on either side. It should be regulated in accordance with extant instructions of Railway Board. A typical cross section is given in sketch -C.

(b) Additional Width of formation will have to be provided to cater for increase in

extra ballast on out side of curves and extra clearance required on double line on account of super-elevation etc.

4.2.4 Adequate Drainage must be ensured for the worst in service conditions. The top

of formation should have cross slope of 1 in 30 from centre of track towards both


sides for single line and from one end towards cess /drain side (single slope) in multiple lines. Further elaboration on drainage is given in para 6.5.

4.2.5 The design should provide for a suitable and cost-effective erosion control

system considering soil matrix, topography and hydrological conditions. Further elaborations have been given in para 6.6.

4.2.6 It will be necessary to keep borrow pits sufficiently away from the toe of the

embankments to prevent base failures due to lateral escapement of the soil. The distance of borrow pit from the bank will have to be decided in each case on its merits. Existing borrow pits, close to toe of bank may be filled or its depth should be taken into account in analysing slope stability of the bank.

4.2.7 In the case of embankments / cuttings in highly cohesive clayey soils, special

treatment may be necessary to ensure a stable formation. Such measures will have to be determined after thorough investigation and study of the soil properties.

4.2.8 Special investigation will also be necessary in regard to high fill construction on

swampy ground or marshy lands and deep cuttings. 4.2.9 In case of all new construction, minimum height of embankment should not be

less than one meter to ensure proper drainage, avoid organic matters and trespassing .

4.2.10 Soils prone to liquefaction falling in gradation zone as per sketch-D. and having

coefficient of uniformity, Cu < 2 should be adequately designed to take care of this.

4.3 Provision of Blanket Layer – Design of Thickness and Selection of Material: To avoid failure of track formation due to inadequate bearing capacity and to safeguard against swelling and shrinking, adequate blanket thickness must be provided in all cases at the time of construction of new lines, permanent diversions, raising of formation, in cuttings etc. or while rehabilitating a failing track formation.

4.3.1 Need for Provision of Blanket Layer & its Functions:

a) It reduces traffic-induced stresses to a tolerable limit on the top of subgrade, thereby, prevents subgrade failures under adverse critical conditions of rainfall, drainage, track maintenance and traffic loadings.

b) It prevents penetration of ballast into the subgrade and also prevents upward migration of fine particles from subgrade into the ballast under adverse critical conditions during service.

c) Its absence or inadequate thickness results in yielding formation and instability. This necessitates high maintenance inputs and leads to increased cost of maintenance. Moreover, crippling speed restrictions may have to be imposed, which adversely affect the throughput.


d) Its absence may result in bearing capacity as well as progressive shear failure of subgrade soil, thereby endangering safety of running traffic.

e) It restricts plastic deformation of subgrade caused due to cyclic stresses induced by moving loads.

f) It results in increased track modulus and thereby reduces track deformations. Consequently, due to reduction in dynamic augment, stresses in rails as well as sleepers are reduced.

g) It facilitates drainage of surface water and reduces moisture variations in subgrade, thereby reducing track maintenance problems.

h) It prevents mud pumping by separating the ballast and subgrade soil. Thus, accumulation of negative pore water pressure in the soil mass is avoided which is responsible for mud pumping.

i) It ensures that the induced stress in subgrade are below the threshold stress of subgrade soil.

j) It ensures dissipation of excess pore water pressure developed in subgrade on account of cyclic loading and leads to increase in shear strength of subgrade soil.

k) It obviates the need for formation rehabilitation work under running traffic at prohibitive cost.

l) It leads to enhanced performance of subgrade as subgrade can serve designed functions more efficiently and effectively.

The quality and depth of blanket material, as specified in these Guidelines, would carry out the above functions satisfactorily under Indian conditions.

4.3.2 Depth of Blanket Layer: Depth of blanket layer of specified material depends primarily on type of subgrade

soil and axle load of the traffic. 4.3.2.1 Depth of blanket to be provided for axle loads upto 22.5t for different types of

subgrade soils (minimum top one meter thickness) has been given as under. In case more than one type of soil exists in top one meter then soil requiring higher thickness of blanket will govern.

Note: Symbols used below for classification of soil at top of sub-grades for

deciding blanket depth is as per IS Classification given in IS:1498. For details, refer Annexure - I.

a) Following soils shall not need blanket:

• Rocky beds except those, which are very susceptible to weathering e.g. rocks consisting of shales and other soft rocks, which become muddy after coming into contact with water.

• Well graded Gravel (GW) • Well graded Sand (SW) • Soils conforming to specifications of blanket material.


Note: Soils having grain size curve lying on the right side of the enveloping curves for blanket material like cobbles and boulders may/may not need blanket. In such cases, need of blanket and, its design should be done in consultation with RDSO.

b) Following soils shall need minimum 45cm thick Blanket:

• Poorly graded Gravel (GP) having Uniformity Coefficient more than 2.• Poorly grade Sand (SP) having Uniformity Coefficient more than 2.• Silty Gravel (GM)• Silty Gravel – Clayey Gravel (GM – GC).

c) Following soils shall need minimum 60cm thick Blanket:

• Clayey Gravel (GC)• Silty Sand (SM)• Clayey Sand (SC)• Clayey Silty sand (SM-SC)

Note: The thickness of blanket on above type of soils shall be increased to 1m, if the plasticity index exceeds 7.

d) Following types of soils shall need minimum 1m thick Blanket :

• Silt with low plasticity (ML)• Silty clay of low plasticity (ML-CL)• Clay of low plasticity (CL)• Silt of medium plasticity (MI)• Clay of medium plasticity (CI)• Rocks which are very susceptible to weathering

4.3.2.2 Soils having fines passing 75 micron sieve between 5 & 12% i.e. for soils with dual symbol e.g., GP-GC, SW-SM, etc., thickness of blanket should be provided as per soil of second symbol (of dual symbol) as per para 4.3.2.1 . For example, if the soil of the subgrade over which the blanket is to be provided is classified as GP - GC then blanket depth for GC type of soil i.e. 60 cm as per para 4.3.2.1 ( c ) is to the provided.

4.3.2.3 Use of geo-synthetics can be considered at places where it is economical to use in combination with blanket as it reduces the requirement of thickness of blanket. It may be particularly useful in cases of rehabilitation of existing unstable formation and in new construction where availability of blanket material is scarce. Use and selection of geo-synthetics should be done in consultation with RDSO.

4.3.2.4 For other types of soil required to be used in subgrade not covered by above clauses, Railways may approach RDSO for getting guidance on deciding blanket thickness depth.


4.3.2.5 For heavier axle load traffic above 22.5t and upto 25t & above 25t upto 30t,

additional blanket thickness of 30cm & 45cm respectively, over and above as given in para 4.3.2.1 of superior quality material, shown as upper blanket layer in sketch "B", should be provided.

4.3.3 Blanket in new lines in light traffic route:

Blanket ensures an important function of reducing induced stresses to acceptable value at top of subgrade. In cohesive subgrades even 100 cycles of repeated load in excess of threshold strength (permissible strength) of subgrade soil will cause failure of formation resulting into large plastic deformations. Therefore, blanket of adequate depth should be provided even for predominantly passenger lines with light traffic.

4.3.4 Specifications of Blanket Material: 4.3.4.1 Blanket material should generally conform to following specifications:

a) It should be coarse, granular and well graded. b) Skip graded material is not permitted. c) Non -plastic fines ( particles of size less than 75 micron) are limited

maximum to 12%, whereas plastic fines are limited maximum to 5%. d) The blanket material should have particle size distribution curve more or

less within the enveloping curves shown in sketch -B. The material should be well graded with Cu and Cc as under: Uniformity coefficient, Cu = D 60/D10 > 4 (preferably > 7) Coefficient of curvature, CC = (D 30)2 / D60 x D10 should be within 1 and 3.

e) The material for upper blanket layer shall be well-graded sandy gravel or crushed rock within the enveloping curves for upper blanket layer as shown in sketch -B.

4.3.4.2 Gradation size analysis and percent fines of blanket material should be determined

using wet sieve analysis as per procedure of IS: 2720 (Part IV) - 1985. 4.3.5 Selection of Blanket Material:

a) Proper survey of area close to projects needs to be carried out to identify suitable sources of blanket material required for the project. Aim of such source identification survey is to use naturally available material, which is cheap and conforms to the specifications laid down.

b) Blanket material could also be obtained by proper blending of two or more soils.

Before approving such sources, trials for blending to judge the final product, needs to be done. Detail methodology of blending to be adopted to produce large quantity of blanket material with consistent quality, needs also to be laid down in advance.


c) Quarry dust or material specifically manufactured through crushers using boulders, rocks, etc. as raw material, conforming to the blanket material specification could also be used as blanketing material.

d) In rare cases, where after studies/trials & survey, blanket material has minor

variation from the laid down specifications, RDSO's guidance could be sought after giving details of trials/studies conducted along with justification and details of soil used for subgrade over which blanket is proposed to be laid.

4.4 Design of Side Slope of Embankment: 4.4.1 Slope stability analysis should be carried out to design stable slopes for the

embankment. Usually, slopes of 2:1 of embankment upto height of 6.0 m would be safe for most of the soils. However, this analysis has to be carried out in detail for any height of embankment in following situations:

a) When subsoil is soft, compressible & marshy type for any depth. b) When subgrade soil (fill material) has very low value of cohesion ' C' ' such that

C'/γH (where H is height of embankment and γ is bulk density of soil) is negligible, i.e., in range of 0.01 or so.

c) When highest water table is within 1.5xH (H is the height of embankment), below ground level, then submerged unit weight of soil below water level should be taken.

4.4.2 In cutting slope, softening of soil occurs with the passage of time, and therefore,

long term stability is the most critical, and should be taken into consideration while designing the cuttings.

4.4.3 Detailed slope stability analysis should be carried out as per procedure laid down in Annexure-III, wherein a typical worked out example of slope stability analysis is also given for guidance. This procedure would be applicable for most of the cases. However, in certain situations, further detailed analysis may be required due to the site conditions, the same may be got done by an expert consultant or matter may be referred to RDSO.

4.4.4 Slope stability analysis may also be carried out using standard computer

programme/software especially made for this purpose. However, the efficacy of the software used should have approval/clearance of RDSO.

4.5 Rehabilitation of Existing Unstable Formations

Existing track foundations, which have failed during service, need special investigations as per para 3.3 and relevant paras of IRPWM. Necessary details should be collected and appropriate rehabilitation scheme should be developed in consultation with RDSO, if required. In general, following points may be kept in view while planning for rehabilitation:


a) In developing rehabilitation scheme, stretches having similar soil characteristics and embankment performance should also be included simultaneously.

b) Cause(s) of unstability of formation should be analysed and accordingly rehabilitation measures formulated. There may be requirement of reprofiling of slope along with laying of blanket.

c) In consultation with RDSO, Geosynthetics may also be used along with laying of blanket, to reduce thickness of blanket if found cost effective.

d) Method of laying of blanket should be appropriate depending upon techno- economical conditions and site requirements.

5.0 MATERIALS FOR CONSTRUCTION:

Construction of embankment is to be carried out normally with soil available in nearby area with proper design of slope and desired bearing capacity. However, there are some soils, which are not normally suitable to be used in construction of new lines as detailed below:

5.1 Unsuitable Soils for Construction:

5.1.1 Soils to be normally avoided are : a) Organic clays, organic silts, peat, chalks, dispersive soils, poorly graded

gravel and sand with uniformity coefficient less than 2, b) Clays and silts of high plasticity (CH & MH) in top 3m of embankment.

5.1.2 Some typical situations, as given below, may arise when in construction

of formation such unsuitable types of soils (para 5.1.1) are not possible to be avoided for economical or any other reason, then Railway may consult RDSO to decide special investigations and other measures to formulate suitable scheme of construction.

a) Cuttings passing through unsuitable soils (para 5.1.1), shales and soft

rocks which become muddy after coming into contact with water, b) Construction of embankment on subsoil of unsuitable types of soils. c) Use of CH & MH type of soils even in top 3m of embankment.

5.2 Use of Mixed Types Soils: 5.2.1 Different types of fill materials, if used, should be deposited in such a way that all

parts of the site receive roughly equal amount of a given material in roughly the same sequence to get approximate homogeneous character of sub-grade.

5.2.2 In situations where soils for construction of embankment consist of cobbles,

boulders, rock or waste fragments etc., largest size of material should normally not be greater than 2/3rd of the loose layer thickness. However, it should be ensured that after every one to three meter of such construction, a 30 cm layer of properly compacted soil (other than soil as given in para 5.1) be provided. A detail slope stability analysis also needs to be carried out to ensure stability of such embankments.


5.2.3 In case cobbles, boulders, etc. i.e., rock materials of bigger size than 2/3rd of the loose layer thickness are only in small quantity, these may be placed on toe of the embankment instead of using as subgrade material.

6.0 EXECUTION OF FORMATION EARTHWORK

Before taking up of actual execution of work, detailed drawings need to be prepared for the entire length of the project to give alignment, formation levels, formation width at ground level, cross sections of catch water drains & side drains, cross section & levels of subgrade, blanket levels, etc. to facilitate smooth execution at site. Execution of work has to be carried out in systematic manner so as to construct formations of satisfactory quality which would give trouble free service. The activities and adoption of good practices involved in execution of earthwork are covered under following headings:-

a) Preliminary worksb) General aspectsc) Compaction of earth workd) Placement of Back-Fills on Bridge Approaches and Similar Locationse) Drainage Arrangement in Bank/Cuttingf) Erosion control of slopes on banks & cuttingsg) Other aspects

6.1 Preliminary Works:

6.1.1 Preparation of Natural Ground:

Preparation of natural ground surface may be carried out as follows:

6.1.1.1 Site clearances: Full formation width at ground level plus additional extra width of 1 m on both sides should be cleared of all obstructions viz. vegetation, trees, bushes, building, fences, abandoned structures etc. and thereafter it should be dressed and leveled. Depressions if any, should be filled with suitable soil duly compacted. Finally, leveled surface should be properly compacted by mechanical means to get leveled and uniform ground surface.

6.1.1.2 When Bank is Constructed On Ground Having Steep Slope then the ground surface should be suitably benched so that new material of bank gets well bonded with the existing ground surface.

6.1.2 Setting out of Construction Limits:

Centreline of the alignment (@ 200 m c/c or so) and full construction width should be demarcated with reference pegs/dug belling about 90 cm away from proposed toe of the bank. Care should be taken not to disturbed the pegs during construction. Pegs should be preferably painted for identification.


6.1.3 Selection of Borrow Area: - a) Borrow area should be selected sufficiently away from the alignment, as for as

possible at the extreme of Railway land but normally not less than 3 m plus height of the embankment to prevent base failure due to lateral escapement of the soil.

b) Borrow area should be selected for soil suitable to be used in construction. 6.1.4 Selection of Fill Material: a) Except for unsuitable soils as explained in para 5.1, any type of locally available

soil can be used as a construction material. OMC & MDD of the selected fill material should be tested in the laboratory as per laid down frequency.

b) Use of material should be planned in such a way that soil with higher percentage of coarse-grained particle is placed on the upper layers of the embankment.

6.2 General Aspects: 6.2.1 A field trial for compaction on a test section shall be conducted on fill material to

assess the optimum thickness of layer and optimum number of passes for the type of roller planned to be used to arrive at desired density. Procedure for field compaction trials is given in Annexure - IV, for guidance.

6.2.2 If the soil has less than required moisture content, necessary amount of water shall

be added to it either in borrow pits or after the soil has been spread loosely on the embankment. Addition of water may be done through flooding or irrigating the borrow areas or sprinkling the water on the embankment through a truck mounted water tank sprinkling system. Use of hose pipe for water need to be avoided.

6.2.3 If the soil is too wet, it shall be allowed to dry till the moisture content reaches to

acceptable level required for the compaction. 6.2.4 Placement moisture content of soil should be decided based on the field trial and

site conditions. The objective should be to compact near OMC to achieve uniform compaction with specified density in most efficient manner.

6.2.5 Clods or hard lumps of soil of borrow area shall be broken to 75 mm or lesser size

before placing on embankment. 6.2.6 Each layer should be compacted with recommended type of roller upto required

level of compaction, commencing from the sides, before putting next upper layer. 6.3 Compaction of Earth Work:

Performance of the embankment would depend to large extent on the quality of compaction done during execution. Need to ensure proper compaction & precautions/ guidelines for this have been given as follows:


6.3.1 Advantages of Compaction: 6.3.1.1 Compaction is the process of increasing the density of soil by mechanical means

by packing the soil particles closer together with reduction of air voids and to obtain a homogeneous soil mass having improved soil properties. Compaction brings many desirable changes in the soil properties as follows:

a) Helps soils to acquire increase in strength in both bearing resistance and

shear strength. b) Reduces compressibility, thus minimising uneven settlement during

service. c) Increases density and reduces permeability, thereby reducing susceptibility

to change in moisture content. d) Reduction in erodability. e) Results in homogenous uniform soil mass of known properties. f) Reduction in frost susceptibility in cold regions

6.3.1.2 However, while compaction of earthwork is a necessary condition to achieve a

stable formation, it does not help in checking against the following causes which needs to be taken care during the design of bank or cutting :

(i) Excessive creep or slipping of slopes . (ii) Swelling and shrinkage characteristic of soils due to variation in moisture content

because physio-chemical properties of a soil do not change on compaction. (iii) Mud pumping at ballast - soil interface. (iv) Settlements due to consolidation of bank and subsoil that can occur even for a few

years after construction of the bank. 6.3.2 Factors Affecting Compaction in the Field:

Compaction of a particular soil is affected by moisture content, compacting effort, type of roller etc as explained below:

(a) Compacting Effort: In modern construction projects, heavy compaction

machinery are deployed to provide compaction energy. Types of machinery required are decided based on type of soil to be compacted. The method of compaction is primarily of four types viz a viz. kneading compaction, static compaction, dynamic or impact compaction and vibratory compaction. Different type of action is effective in different type of soils such as for cohesive soils, Sheepsfoot rollers or pneumatic rollers provide the kneading action. Silty soil can be effectively compacted by Sheepsfoot roller/pneumatic roller or smooth wheel roller. For compacting sandy and gravelly soil, vibratory rollers are most effective. If granular soil have some fines both smooth wheeled and pneumatic rollers can be used.

(b) Moisture Control: Proper control of moisture content in soil is necessary for

achieving desired density. Maximum density with minimum compacting effort can be achieved by compaction of soil near its OMC (Optimum Moisture


Content). If natural moisture content of the soil is less than the OMC, calculated amount of water should be added with sprinkler attached to water tanker and mixed with soil by motor grader for uniform moisture content. When soil is too wet it is required to be dried by aeration to reach up to OMC.

(c) Soil Type: Type of soil has a great influence on its compaction

characteristics. Normally, heavy clays, clays and silts offer higher resistance to compaction, whereas, sandy soils and coarse grained or gravelly soils are amenable for easy compaction. Coarse-grained soils yield higher densities in comparison to clay. A well-graded soil can be compacted to higher density.

(d) Thickness of Layer: Suitable thickness of soil of each layer is necessary to

achieve uniform compaction. Layer thickness depends upon type of soil involved and type of roller its weight and contact pressure of its drums. Normally, 200 – 300 mm layer thickness is optimum in the field for achieving homogenous compaction.

(e) Number of Passes: Density of soil will increase with the number of passes of

roller but after optimum number of passes, further increase in density is insignificant for additional number of passes. For determination of optimum number of passes for given type of roller and optimum thickness of layer at a predetermined moisture content, a field trial for compaction is necessary as explained in Annexure -IV.

6.3.3 Compaction Procedures for Different Soils:

The embankments are constructed with locally available soils provided it fulfils the specified requirements. Procedure of compaction to be adopted will depend on the type of soil being used in construction. General guidelines to deal with compaction of various types of soils for attaining optimum dry density/relative density at minimum effort, have been briefly given as under:

6.3.3.1 Compaction of Cohesion Less Gravely and Sandy Soil: i) Sandy & gravely soils should be compacted with vibratory rollers. If fines are

less in these types of soils, it can be compacted with minimum number of passes of vibratory rollers without strict control of moisture to achieve desired Relative Density. With higher percentage fines, sandy and gravely soils need to be brought to OMC level to get effective compaction. Uniformly graded sand and gravel are difficult to be compacted. Top layer of sand and gravel remains loose in vibrating compaction. Therefore, in final pass the roller should move smoothly without vibration. Dry densities attained in field trails normally should be around MDD/ specified Relative Density as obtained from laboratory tests and should form the basis for specification and quality control.

ii) Poorly graded sand and gravel with Cu < 2.0, should not be used in earthwork for

the banks to safeguard against liquefaction under moving loads or especially due to earthquake tremor. Generally, fine sand is prone to liquefaction. Materials


having gradation as per sketch ‘D’ should be specifically examined and designed to prevent possibility of any liquefaction.

6.3.3.2 Compaction of Silty - Clayey Soils:

Silty soil is a fine-grained soil. These can be plastic or non-plastic depending upon the clay content in it. Silts and fine sands with high water content have a tendency to undergo liquefaction under vibrating rolling due to the pore water pressure generated by mechanical work. Silty soils can be compacted satisfactorily near about OMC either with smooth rollers or vibratory rollers. Vibratory roller will give high degree of compaction and higher lift. Compaction of silty clays will have to be handled in a manner similar to clays.

6.3.3.3 Compaction of Clays:

i) Water content plays very important role in compaction of clays. Main objective ofcompacting predominantly clays is to achieve uniform mass of soil with no voids between the lumps of clays. If moisture content is too high, roller tends to sink into the soil and if too low the chunks would not yield to rolling by rollers. Appropriate water content i.e. OMC of the soil is in the range of about plastic limit plus two percent. Sheepsfoot rollers are most effective in breaking the clods and filling large spaces.

ii) Thickness of layer should not be more than depth of feet of roller plus 50 mm.Pad foot vibratory roller with drum module weight of 7tonne( total static weightof 11 tons) for a lift thickness of 30 cm is found quite effective for compaction ofclays. For better results, initial rolling with static pad foot roller followed by 15tons vibratory roller can be tried.

6.3.4 In case of such soils, the MDD and OMC, as determined in the Laboratory my not be very relevant and therefore achievable MDD and practicable moisture content at which such soils can be compacted effectively should be determined by conducting field trials.

6.3.5 Selection of Compacting Equipment:

The performance of roller is dependent mainly on type of soil used in construction. Guidelines on selection of compacting equipment are given in Annexure V. Vibratory rollers which can be used in static as well as dynamic mode with plain & pad drum, are now being manufactured by reputed Indian Companies also. Salient features of some of models are given in Annexure- VIII.

6.4 Placement of Back-Fills on Bridge Approaches and Similar Locations:

6.4.1 The back fills resting on natural ground may settle in spite of heavy compaction and may cause differential settlements, vis-a-vis, abutments, which rest on comparatively much stiffer base. To avoid such differential settlements, while on


one hand it is essential to compact the back fill in the properly laid layers of soil, on the other hand, the back fill should be designed carefully to keep;

i) Settlements within tolerable limits. ii) Coefficient of subgrade reaction should have gradual change from

approach to the bridge. 6.4.2 Back-fills on bridge approaches shall be placed in accordance to para 605 of

Indian Railways Bridge Manual 1998. Details given at Fig I. 6.4.3 Fill material being granular and sandy type soil, therefore need to be placed in

150mm or lesser thick layers and compacted with vibratory plate compactors. 6.4.4 While placing backfill material benching should be made in approach

embankment to provided proper bonding. 6.5 Drainage Arrangement in Banks and Cuttings:

Drainage is the most important factor in the stability of bank/cutting in railway construction. Effective drainage of the rainwater in the monsoon season is very important to safe guard bank/cutting from failure. Railway formation is designed for fully saturated condition of soil. However, flow of water should not be allowed along the track as it not only contaminates ballast but also erodes formation. Stagnation of water for long time on formation is not desirable. Therefore, drainage system should be efficient enough to prevent stagnation and allow quick flow of water. Some guidelines on this aspect are given as follows:

6.5.1 Drainage of Embankment: In bank cross slope is provided from center towards end to drain out surface water. Therefore, normally there is no need of side drains in case of embankment. However, there are situations where height of bank is such that blanket layer goes below normal ground level. In such cases, side drains may require to be constructed along the track at suitable distance so that track alignment does not become channel for flow of ground surface water.

In case of double line construction, central drain between the tracks should be avoided to extent possible (even if it means resorting to additional earthwork to facilitate flow of water) as it is not only difficult to construct but also difficult to maintain for continuous vibrations caused by moving traffic, problem in proper curing of concrete etc. Only in very rare situations, when drainage of water is not possible without construction of drain, suitable arrangements for construction of drain with pre-cast concrete channel/ subsoil drains alongwith proper outfall should be made. If distance between adjacent tracks is large enough, suitable slope should be provided in ground to make rain water flow in natural manner. Wherever, there is level difference between two adjacent tracks, suitable non-load bearing dwarf wall may be constructed to retain earth.

6.5.2 Drainage in Cuttings: 6.5.2.1 Side Drains: In case of cuttings, properly designed side drains of required water

carrying capacity are to be provided. If height of the cutting is less (say, up to


4m), normally only side drains on both sides of the track are to be provided. In case of deep cuttings, catch water drains of adequate water carrying capacity are also required along with side drains. A typical sketch of side drain and catch water drain has been given in Sketch - E. It is to be noted that blanket material is to be placed like fill/embankment and top of side drains has to remain below the bottom of blanket material.

6.5.2.2 Catch Water Drains: Surface water flowing from top of hill slope towards the

track in huge quantity needs to be controlled on safety consideration. It is also not possible to allow water from the hillside to flow into the side drains, which are not designed for carrying such huge quantity of water. Therefore, it is essential to intercept and divert the water coming from the hill slopes, accordingly, catch water drains are provided running almost parallel to the track. Depending on site condition, water from the catch water drains may require be diverting by sloping drains and carrying across the track by means of culvert. In some of the situations, depending on topography of top of cutting, there may be requirement of construction of net of small catch water drains which are subsequently connected to main catch water drain so that there is no possibility of water stagnation/ponding upto distance approximately three times depth of cutting from its edge. Catch water drains should be made pucca/lined with impervious flexible material locally available.

a) Considerations in Design of Catch Water Drains: These should be properly designed, lined and maintained. If catch water drains are kuchha/ broken pucca drains, water percolates down to the track through cracks, dissolving the cementing material resulting into instability in the cuttings. Catch water drains should be located slightly away (as per site conditions) from the top edge of cutting and water flow should be led into the nearby culvert or natural low ground. Some additional salient features to be observed are as follows:

i) Catch water drains shall have adequate slope to ensure development of self-

cleansing velocity. ii) Catch water drains shall not have any weep hole. iii) The expansion joints, if provided, shall be sealed with bituminous concrete. iv) Regular inspection and maintenance work, specially before onset of monsoon,

should be carried out to plug seepage of water. v) Catch water drains shall have well designed out fall with protection against

tail end erosion.

Though capacity and section will depend on terrain characteristics, rainfall etc. but following parameters are important for design of catch water drains:

• Intensity and duration of rain fall. • Catchment area- shape, size, rate of infiltration etc. • Velocity of flow which should satisfy the Manning’s formula • Minimum gradient of drain should be in range of 1 in 400 to 1 in 700.


• Normally catch water drains should trapezoidal cross section. • The catch water drain should not be given gradient more than about 1 in 50

(but in no case more than 1 in 33) to avoid high water velocity and possibility of washout of lining material

• Rugosity coefficient should be about 0.03. b) Alignment plan, longitudinal section and soil survey records of catch water

drain should be updated from time to time as per development in the area of influence.

6.6 Erosion Control of Slopes on Banks and Cuttings

Exposed sloping surface of bank/cutting experiences surfacial erosion caused due to the action of exogenous wind and water resulting into loss of soil, leading to development of cuts, rills/gullies adversely affecting the cess width, soil matrix, steepening of slopes etc which depends on type of soil, climatic conditions, topography of area, length of slope etc.

Erosion control measures are commonly classified in following categories: a) Conventional non-agronomical system, b) Bio-technical system, c) Engineering system, and d) Non- conventional hydro-seeding system.

Most common methods used are the Bio-technical and Engineering System. However, appropriate method needs to be decided depending on site conditions. These methods are explained in following paras

6.6.1 Conventional Non-agronomical System: This system uses asphalting, cement stabilisation, pitching etc. This method is best

utilized against seepage, erosion by wave action etc. 6.6.2 Bio- Technical Solution:

In this system, vegetation is provided on exposed slopes. It is suited for soil with some clay fraction. Method consists of preparing slope area by grading it for sowing seeds or planting root strips of locally available creeping grass. It’s root goes upto 50 to 75mm deep into the slopes serving as a soil anchor and offering added resistance to erosion. Some typical species of grass which develop good network of roots and considered suitable are listed below: - Doob grass - Chloris gyne - Iponea gorneas (Bacharum Booti) - Casuariva and goat foot creepers etc. - Vetiver grass (vetiveria zizanioides)

6.6.2 Engineering System:

In this system, three methods, as mentioned below, are normally used.


a) Geo-jute : In this system, geo-jute is used. The system is used in areas havinghigh erosion problems. Geojute is eco-friendly material made of jute yarn with acoarse open mesh structure and is biodegradable. On degradation, it helps ingrowth of vegetation. It is of two types i.e. fast biodegradable and slowbiodegradable. The methodology by which geojute on slopes of banks/cuttingsshould be provided is explained as follows:

• Top 50 to 75 mm soil should be made free of clods, rubbish, large stones etc.• Top surface should be properly dressed.• Seeding should be done by distributing evenly over the slope.• Folded geojute should be buried at critical slippage of top soil.• Geojute is then unrolled loosely and evenly.• Up channel and shoulder are buried and stapled and then anchored as per the

requirement of the supplier.• Down channel ends and toes are folded and secured as per manufacturer's

requirement.• Wherever it is getting terminated, it should be buried as per specification.• Longitudinal edge overlapping should be as per manufacturer's requirement

and stapled at one meter interval.• Rolled junctions are overlapped as per manufacturer's requirement.• Up channel section over down channel additional row of staples is fixed at 1m

interval down each strip.

Watering facility should be ensured during initial period of sowing if the work is undertaken during non-monsoon period. Post laying protection against stamping and grazing by cattle is required. In case of any damage, local spot repair should be carried out. Once vegetation is well established, no maintenance is required.

b) Polymer Geogrids: Under unfavourable soil and rainfall conditions wherevegetative growth is difficult or is considered inadequate, a synthetic rootreinforcement vegetation system using geogrids should be provided. Geogrids areflexible, non biodegradable, resistant to chemical effects, protected againstultraviolet degradation and are stable over a temperature of 60-100 ˚C. Itprovides root matrix reinforcement with dense vegetation growth which works aspermanent measure against erosion. Simply extruded un-oriented and unstretchedpolymeric grids of low mass are considered adequate. In deep open cuttings withboulder studded strata , bi-axially oriented geogrids of low mass should bedeployed with suitable anchors to retain the boulders in place till growth ofvegetation is adequate. Following methodology should be adopted for laying atsite.

Slope area should be dressed with filling of cavities and pot holes if any by light ramming. The net should be unrolled ensuring uniform surface contact. Geogrid ends at top and bottom of slopes should be suitably anchored in 50cm x 50cm size trenches. MS pins 6mm dia and 2m c/c should be used to hold the light weight net in position for an initial period of 2 to 3 months. Overlapping of grids (about 75mm) and jointing with 6mm dia, ultraviolet stabilised polymer braids is


required to be carried out in longitudinal direction of laying. No overlaps are required in transverse direction of laying while jointing.

6.6.4 Hydro-seeding System:

This is non-conventional and innovative system of development of vegetation. This system can be tried on mountainous slopes and steep banks/cuttings. In this system, Verdyol mulch solution @ 100 to 150 gm/m2 is sprinkled on the surface for germination of vegetation depending upon the local soil and the climatic conditions.

6.6.5 Protection of Slopes in Cutting:

a) The causes and manifestations of surfacial erosion of slopes of banks and cuttings are almost similar. In case of cuttings, where the slopes are normally steeper than those of banks, special protection measures would be necessary. For cutting slopes steeper than 1:1 with soil conditions favorable for vegetative growth, turf sodding (size 20x20x7.5cm) should be transplanted from adjoining grassed area. To prevent slipping tendency of sodding patches, especially during rains, these should be anchored with wooden pegs.

b) In case of cutting slopes, having exposure of medium to large size boulders

embedded in erodable soil, special protection measures may be required till the growth of vegetation takes place. Low to medium strength (13 to 22 kN/m) and biaxially oriented geogrids should cover the exposed boulders studded slopes and suitably anchored. Prior to adequate vegetation growth, surfacial erosion developing dislodging tendency of small to medium sized boulders could be checked with the help of polymer nets.

6.7. Other Aspects of Construction of Earthwork 6.7.1 Execution of Earthwork- General aspects a) The spreading of material in layers of desired thickness over the entire width of

embankment should be done by mechanical means and finished by a motor grader. The motor grader blade shall have hydraulic control suitable for initial adjustment and maintain the same so as to achieve the slope and grade.

b) Thickness of layer is decided based on field compaction trials. However, as a good

practice thickness of layer should be generally kept as 300 mm for fill material and 250 mm for blanket material in loose state before compaction.

c) If natural moisture content (NMC) of the soil is less than the OMC, calculated

amount of water based on the difference between OMC & NMC and quantity of earthwork being done at a time, should be added with sprinkler attached to water tanker and mixed with soil by motor grader or by other means for obtaining uniform moisture content. When soil is too wet, it is required to be dried by aeration to reduce moisture content near to OMC. Efforts should be made to keep


moisture content level of the soil in the range of OMC ± 2% at the time of compaction.

d) Fill shall be placed and compacted in layers of specified thickness. The rate ofprogress should be, as far as possible, uniform so that the work is completed tofinal level almost at the same time.

e) The rolling for compaction of fill material should commence from edges towardscenter with minimum overlap of 200 mm between each run of the roller. In finalpass, roller should simply move over the surface without vibration so that topsurface is properly finished.

f) Extra bank width of 500 mm on either side shall be rolled to ensure propercompaction at the edges. The extra soil would be cut and dressed to avoid anyloose earth at the slopes. This should preferably be done with help of grade cutter.

g) At the end of the working day, fill material should not be left uncompacted. Careshould be taken during rolling to provide suitable slope on top of the bank tofacilitate quick shedding of water and avoid ponding on formation.

h) During construction of formation, there may be rainfall to the extent that rain cutsmay develop on the surface of formation due to erosion of soil. Care should betaken that these rain cuts are not allowed to develop wide and deep otherwisethese locations will remain weak spots. Provisions should be made in contractconditions to attend / repair such rain cuts , as a regular measure.

i) Top of the formation should be finished to cross slope of 1 in 30 from one end toother towards cess/drain in multiple lines and from center of formation to bothsides in single line.

j) Once the top surface of the formation has been finished to proper slope and level,movement of material vehicle for transportation of ballast, sleepers etc. should beavoided, these movements will cause development of unevenness, ruts on thesurface which will accumulate water and weaken the formation. The methodologyof transportation of P. Way material needs to be planned.

k) In conversion/doubling/rehabilitation projects, suitable benching of existing slopeshall be done before new earthwork is taken up to provide proper bondingbetween old and new earthworks. It should be ensured that there is no humusmaterial left on the benched slope. Care needs to be taken to avoid entry ofrainwater into the formation from this weak junction., otherwise this would resultin development of weak formation, slope failure, maintenance problem due touneven settlement etc.

l) At locations where the water table is high and the fill soil is fine-grained, it maybe desirable to provide a granular layer of about 30 cm thickness at the base,above subsoil across the full width of formation.


m) At the places where embankment materials are not conducive to plant growth, topsoil obtained from site clearance as well as top layer of borrow pit which is rich inorganic content and suitable for plant growth, may be stored for covering slopes ofembankment & cutting after construction, or other disturbed areas, where re-vegetation is required, as far as practicable.

6.7.2 Widening of Embankment:

Before taking up widening of existing of embankment for gauge conversion, it should be ensure that remedial measures for unstable formation have been taken.

i) All vegetation shall be uprooted and taken away from the site of work. The loosematerials removed from the slope should be dumped to form the bottom mostlayer on the ground in the width to be widened. If required, it shall besupplemented with local granular soil.

ii) Starting from the toe, benching on the slope at every 30cm height shall beprovided on the slope surface as in Sketch-E, so as to provide properamalgamation between the old and new earthwork.

iii) Earthwork shall be carried out in layers, each layer sloping out 1:30 andcompacting it mechanically using vibratory rollers of around 0.9m width (whichare available in the market), 6 to 8 passes of such rollers shall usually suffice toprovide the compaction to the specified level.

iv) The width of each layer of earthwork shall be in excess by 300mm of the designedprofile to enable compaction near the edges. The excess width, thereafter, cut anddressed, so as to achieve the required bank profile.

v) Earthwork shall be completed upto designed formation level keeping dueallowance for the blanket if need be.

6.7.3 Raising of Existing Formation:

After widening of the bank to the level of the existing formation, raising shall be done as under:

i) Raising less than 150mm shall be done with ballast, restricting overall thickness to350mm.

ii) Raising from 150mm to 1000mm, the existing ballast shall be taken out undersuitable speed restriction and raising should be done in suitable steps with thematerial as per specification of blanket material, preferably that of upper blanketlayer. After raising to the desired level, clean ballast shall be inserted.

iii) Raising of more than 1000mm, under traffic, would not be cost effective and itmay be desirable to lay a detour for passage of traffic temporarily. Final decisionshall, however, be based on economic considerations.


6.7.4 Earthwork in New Detours:

To facilitate easing out of existing sharp curves, change of gradients and rebuilding of important bridges, new detours shall be necessary. Design and construction of such detours shall be carried out in accordance with this provisions in the Guidelines.

6.7.5 Use of Construction Equipments for Execution of Earthwork

Any manual methods of construction cannot achieve the desired quality of earthwork. It would be necessary to deploy modern equipments such as earthmover, motor graders, scraper, dumpers, mobile water sprinklers, vibratory rollers, sheepfoot rollers etc. as per need, on all projects, so that the quality of work is as per laid down standards. It would be desirable to maintain records of work done by various equipments at a particular site to assess the out put and quality control.

6.7.6 Construction of New Formation over Soft Compressible Sub-soil:

Various methods such as i) pre- loading and stage construction, ii) installation of vertical sand drains, and iii) installation of prefabricated vertical drains are available for strengthening of such weak soil by expediting consolidation. Selection of a particular method for safe construction of embankment will basically depend on rate of construction. Therefore, depending on site requirement and techno-economic considerations, a particular method for construction may be decided in consultation with RDSO.

6.7.7 Sandwich Construction of Banks with Cohesive Soils:

Sandwich type of construction may be adopted for construction of embankments with cohesive soils having very low permeability (less than 10 –2 cm/sec.) and where height of bank is greater than 3m. In such situations, a layer of coarse sand ( Cu > 2) of about 20 to 30 cm thick should be provided at bank height intervals of 2 to 3m. Sketch –G provides Guidelines for sandwich construction for different heights to improve factor of safety against slope failure, drainage and dissipation of pore water pressure. It is desirable to have a bottom layer of coarse sand in all cases where soils of low permeability is used even for depths upto 3m. However, before adopting such construction, it may be necessary to carry out a detailed technical study alongwith economics of sandwich construction, depending on site conditions and availability of material, if required, in consultation with RDSO.

6.7.8 Safety at Work Site:

Necessary precautions towards safety at work site, including doubling and gauge conversion, should be part of the contract document. Similarly, safety for staff working at site should be carefully ensured to avoid any untoward incidence. To the extent possible, the safety instructions are to be suitably incorporated in the


contract document with clear understanding of responsibility of concerned staff and contractor about their responsibility.

6.7.9 Environmental Aspects:

Efforts should be made to ensure least disturbance to surrounding environment, to the extent possible. Wherever, there has been disturbance due to large scale construction, efforts need to make to improve the surroundings and environment by way of massive group plantation, so as to restore the area. Rules and regulations of the government in vogue, in regard to the environment, need to be followed.

7.0 QUALITY ASSURANCE OF EARTHWORK

To achieve effective performance of permanent assets created in New line/Doubling/Gauge Conversion projects, adequate quality control/checks at all stages of construction viz. selection of construction materials, adoption of method, use of suitable machinery for construction and during execution of work is essential. Following quality control system needs to be adopted during execution of earthwork.

7.1 Setting up of GE Lab at Construction/Rehabilitation Site

A well-equipped GE Field Laboratory shall be set up at all construction projects connected with new lines, doubling and gauge conversion works as well as, where rehabilitation of failing formation is being undertaken. Number of such GE labs to be established on a particular project/work site would depend on the pace and length of work being executed at a particular site and the output of the lab so that all quality control checks can be performed effectively. The field lab should be manned adequately by trained official & staff capable of carrying out required investigation, soil testing and quality control at site.

a) Aspects to be looked after by field GE lab are as under:

i) To ensure that the quality of supplied soil and blanket material conformsto the accepted limits of gradation, classification, plasticity, etc.

ii) To evaluate method of compaction by conducting tests in connection withfield trials.

iii) To exercise moisture and density control as the earthwork proceeds inlayers rolled with the suitable equipment.

b) Depending on the requirement, field lab shall be equipped with minimumequipments as listed in the Annexure-X to facilitate the following minimum tests:

i) Gradation Analysis-Sieve and Hydrometer.ii) Atterberg’s limits - liquid limit & plastic limitiii) Optimum Moisture Content (OMC), Maximum Dry Density (MDD) and

Relative Density.iv) Placement moisture content & in-situ Density.


7.2 Quality Check of Earthwork

Quality of execution of formation earthwork shall be controlled through exercise of checks on the borrow material, blanket material, compaction process, drainage system and longitudinal & cross sectional profiles of the embankment. The summery of quality control of Earthwork has been given in Annexure – VII. The details of quality control procedure are as follows:

7.2.1 Quality Control on Construction Material:

This is required to ascertain the suitability of the material for construction of embankment and to decide the OMC and MDD, which become the quality control inputs for compaction control. Control tests are required to be done for borrow material as well as blanket material.

7.2.1.1 Borrow Material :

Fill material proposed to be used either from Railway land or from outside would have to be assessed for its suitability as well as to decide thickness of blanket layer, after conducting soil classification and other relevant tests as per site requirement. Further tests, if needed, should be performed as directed by engineer in-charge to fully assess the material. On the basis of the tests, areas for borrow material, especially from outside the Railway land, needs to be earmarked. Once the material has been found fit for use as fill material for embankment, further lab tests, to assess OMC, MDD/ Relative Density, need to be conducted. In case, slope stability analysis, as explained in para 4.4 is required, triaxial test will also be done to find effective shear parameters. It would be in the interest of the execution agency to have frequent tests conducted on his own to judge the suitability of the material to avoid any complication at a later stage. However, the final acceptance of the borrow material should be at the site where it is laid, as follows:

(a) Frequency of Testing at Site: At least one test at every change of soil strata subject to minimum of one test for every 5000 cum to assess suitability of fill material and to lay down OMC and MDD/Relative Density.

(b) Acceptance Criteria: Materials conforming to para 5.0 need only to be used for construction of embankment.

7.2.1.2 Blanket Material:

The source of blanket material, detailed in para 4.3.4.2, needs to be identified based on tests & studies conducted and conformity of the material to the Specification as laid down in para 4.3.4. It would be desirable to have a check on quality of material at source/manufacturing point so that major deviation in quality of the material being sent to site does not exist. It would be in the interest of the supplier to have such tests conducted on his own to avoid any complication at a later stage. The frequency of such test could be laid down by the engineer in-


charge, if need be. However, the final acceptance of the blanket material should be at the site where it is laid, as follows:

(a) Frequency of Tests at Site: Minimum one test per 500 cum or part thereof.

(b) Method of Test: Blanket material should be tested as per IS: 2720 (Part 4) to plot particle size distribution curve, so as to assess its suitability. It would be necessary to carry out wet analysis to assess actual percentage of fines. To expedite testing work, dry sieve analysis may be carried out if variation between results of dry and wet analysis are not significant and adequate margin exists with respect to acceptance criteria. However, in such cases also, wet analysis has to be carried out at frequent interval to verify the extent of variation. In any situation, acceptance of blanket material would be based on wet analysis only. The samples for wet analysis should be prepared as per para 4.3 of IS: 2720 (Part 4).

(c) Acceptance Criteria : The material should generally conform to specification as given at para 4.3.4.

7.2.2 Quality Control Checks on Finished Earthwork:

7.2.2.1 Compacted Earth: Degree of compaction of each layer of compacted soil should be ascertained by measurement of dry density/Relative Density of soil at locations selected in specified pattern. The method of sampling, frequency of tests, method of tests to be conducted and acceptance criteria to be adopted are as under

a) Method of Sampling :

i) Various methods of selection of sample points for check of in-situ dry density arein vogue. These are shown in sketch-H. The sampling adopted has to be such thateffectiveness of proper compaction having been done for the entire area underconsideration can be judged.. For this, the Engineer in-charge should lay downthe method adopted in detail depending on site conditions and accordingly recordsof checks done are properly maintained. However, in absence of such procedurelaid down, following method should be adopted:

Suggested Method of Sampling: For each layer, a minimum of one sample at apredetermined interval (in compliance with the requirement stated in next para)along the centreline of the alignment, would be taken in a staggered pattern so asto attain a minimum frequency of tests as given in the para 7.2.2.1(b). Forsubsequent layer, the stagger should be such that the point of sampling does notfall vertically on the earlier sampling points of the layer immediately below. Theprocess of sampling is explained in Sketch-H for guidance. Additional samplingpoints can be taken, as considered necessary.

ii) In case of bank widening, sampling should be done at an interval of minimum200metres on widened side(s) of embankment.


b) Frequency of Tests: Density check would be done for every layer of compactedfill/blanket material as per following minimum frequency :

i) At least one density check for every 200 sq.m for blanket layers and top onemetre of sub-grade.

ii) At least one density check for every 500 sq.m.for other than blanket and onemetre of sub-grade.

In case of bridge approaches or special locations closer frequency may be adopted.

c) Method of In-situ Dry Density Measurements : Any of the following methodscould be adopted as per the requirements at site.

Method of measurement

Procedure of test

Parameters to be measured

Remarks

i) Sand Replacement Method

As per IS-2720

GUIDELINES FOR EARTHWORK IN RAILWAY PROJECTSiricen.gov.in/iricen/other_manual/GE-G1 Guidelines...

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